A rat penetrating keratoplasty model was developed to evaluate the corneal allograft rejection reaction. Using Brown Norway rats as donor for Lewis rats and by not removing sutures, a rejection rate of approximately 90% could be seen by the third week. Inflammation of the grafts could be seen in the second week followed by vascularization. Monoclonal antibodies to T- lymphocyte subsets and major histocompatibility complex (MHC) antigenic markers in the rat are now available which allow for the delineation of the acute corneal rejection reaction.